1. Field of the Invention
The present invention relates to an ink-jet printing apparatus for performing printing by ejecting ink.
2. Description of the Related Art
An ink-jet printing method is becoming a major printing method for features of high speed, high image quality and quietness. One example of the construction of the ink-jet printing apparatus is shown in FIG. 9. In FIG. 9, reference numeral 6 denotes a head for ejecting ink for printing, 7 denotes a tank for storing the ink to be supplied to the head 6, 8 denotes a platen for holding a printing medium, 9 denotes a recovering means for maintaining good printing condition. In the ink-jet printing method, printing is performed by ejecting the ink through ejection openings of fine nozzles. Therefore, when dust is deposited on the surface of the head 6 where the ejection openings are formed, ejection of the ink can be blocked to cause defects in printing. Also, by continuously repeating printing, the ink which does not reach the printing medium, may deposit on the ejection opening forming surface to cause deflection of the ejecting direction of the ink.
The recovering means 9 is provided for maintaining good condition in ejection of ink even in the case set forth above. In general, the recovering means comprises a wiping member for wiping off the dust, residual ink droplets and so forth by sweeping the ejection opening forming surface of the head 6, a pump for sucking ink through the ejection opening of the head for cleaning the ejection opening forming surface, and so forth.
However, in the prior art, upon operation of the recovering means 9, it is possible to cause damaging or wearing of the ejection opening forming surface by the wiping member, or to reduce amount of the ink to be used for printing since the ink is sucked from the ejection opening for disposal. In this respect, it is desirable to minimize the recovery operation by the recovering means 9 so that recovery process may be performed just before occurrence of failure.
Therefore, there have been proposed a method for determining a timing of recovering operation by detecting a temperature of the head, or a method for determining the recovering operation by counting a signal amount to be printed in a printing memory as disclosed in Japanese Patent Application Laid-open No. 64890/1993. On the other hand, technology is directed to high definition and high speed printing to inherently require a greater number of nozzles in the head 6 for increasing the number of dots to be printed simultaneously. Conventionally the head has in the order of 64 nozzles, but a head having 500 to 1000 nozzles and furthermore, a line head having 3000 to 4000 nozzles have also been proposed in the recent years.
However, in such a multi-nozzle head, it often causes fluctuations of frequency of use in each nozzles. In such case, it is not possible to determine the optimal timing to effect recovering operation only by detecting the temperature of the head 6 or by counting the data in the printing memory, resulting in increasing possibility of causing defects in printing.
FIG. 10 shows the number of printing dots per nozzle when printing operation is performed for a certain period after the latest recovering operation. FIG. 10A is the case where no significant difference of frequency of use among the nozzles is present and where sufficient margin is present to the region where failure of ejection is potentially caused. FIG. 10B is the case where a significant difference of frequency of use among the nozzles is present, the average number of dots is the same as that of FIG. 10A and where not all but some of the nozzles have reached the region where failure of ejection is potentially caused. In the event that an interval of recovering operation is simply shortened for avoiding the ejection failure, the amount of the ink to be disposed is increased, the possibility of damaging and/or wearing of the printing head is increased and throughput of the printing apparatus is lowered.